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You could blame some of Utah's wildfires on bad judgment  starting a hot engine on dry grass or target shooting on parched hillsides.

You could point to bad luck, namely lightning and wind.

But there is another culprit in all the blazes: climate change.

That's the assessment in a white paper last week from climate scientists.

"Climate change is clearly playing a role," said Kevin Trenberth, who leads the Climate Analysis Section at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. "There are wildfires all over the place."

Trenberth and his fellow scientists  Jerry Meehl, also of NCAR; Jeff Masters, of Weather Underground; and Richard Somerville, of the University of California-San Diego's Scripps Institution of Oceanography  said their review of new research shows a pattern that points to a warmer world and, in the West, a drier, fire-prone one.

"Higher spring and summer temperatures, along with an earlier spring melt, are also the primary factors driving the increasing frequency of large wildfires and lengthening the fires season in the Western U.S. over recent decades," they summarize. "The record-breaking fires this year in the Southwest and Rocky Mountain region are consistent with these trends."

Trenberth is internationally known for his assertions that recent trends show climate change is playing out in dramatic ways at an unprecedented pace.

Though some call his conclusions controversial, the observational data his team cites are straightforward. They are taken from NASA, the National Oceanographic and Atmospheric Administration and peer-reviewed scientific studies.

Heat waves  periods of days to weeks of abnormally toasty temperatures  used to come along every 20 years on average, the scientists said. Nowadays, they occur more frequently, every 10 years, and they are projected to pop up as often as every other year by century's end, according to the Heat Waves and Climate Change white paper published Thursday.

"These dry spells," Trenberth said Saturday in an interview, "tend to get more intense and last longer."

Another factor in the wildfires is the dry spell that has settled in. In most of Utah, Nevada, Colorado, Wyoming and New Mexico, precipitation has been 30 percent to 95 percent lower than normal, according to NOAA data covering March through May.

He called water the "air conditioner for the planet," noting that melt and evaporation carry heat off the ground under normal conditions. But this year the vegetation hasn't had that cooling benefit because of the warm spring.

The problem hit home last week at the Boulder research center, where Trenberth works, when a lightning blaze broke out and forced the evacuation of the facility for two days.

"I have no doubt climate change is playing a role in this," he said.

Judy Curry, a climate scientist at Georgia Tech, said there is not enough evidence to link the current hot, dry conditions to climate change.

"This is not like something unique in recent history," she said, pointing to the Dust Bowl conditions of the 1930s. "There's a lot of natural variability in the climate.

"There's probably some human contribution," she added, "but to sort out what's human versus what's natural is difficult, and it's not clear it makes sense to try to do that."

Shelby Law, a meteorologist with the U.S. Bureau of Land Management in Utah, is focused on the trend on the parched range and forests across Utah.

"It's dry," she said. "It just burns."

It's a stark contrast to the past few years, when we've had fewer-than-usual wildfires.

With official drought conditions in almost all of the state and lightning expected midweek, Law said the message for the Utahns is simple: "They need to know fire danger is setting records this year."

Mike Jenkins, a forest expert at Utah State University, agreed that everyone should pay attention because of the unusually low soil moisture.

"If what [climate scientists] predict is true," he said, "this would be the scenario we'll see more of in the future."

fahys@sltrib.com 

The fires so far

Utah wildfires have erupted 438 times this year and burned more than 108,000 acres so far. Lightning started 45 of those blazes. Humans caused 393 of them